The present invention relates to a drive mechanism. More particularly, the present invention relates to drive mechanism for use with an overhead shaft of a sectional door, such as garage doors and the like, for raising and lowering the door, the drive mechanism having an integrated ratchet mechanism and acting also as a safety braking device for preventing an uncontrollable raising and/or lowering of the sectional door.
It is known in the art that commercial and residential sectional garage doors usually require counterbalancing mechanisms to counterbalance the weight of the door in order to decrease the force required to open the door and also facilitate its closing from a raised to a lowered position. Large sectional garage doors used in commercial and residential applications may be manually or power operated. In either case, but particularly for manually operated doors, counterbalancing mechanisms have been used for many years to counterbalance the weight of the door and control its opening and closing movements so that one person can control the operation of the door more easily. Counterbalancing mechanisms are also advantageous for power operated overhead doors since they reduce the power requirements needed for the motor and they lower the structural strength required for the door opening and closing mechanism. In other words, lighter weight, lower cost, door controlling mechanisms, such as chain hoists for example, may be used if a counterbalancing mechanism is connected to the door to assist it in its opening and closing movements. Furthermore, the provision of a counterbalancing mechanism minimizes the chance of a rapid and uncontrolled closing of the door in the event of a failure of the door opening and closing mechanism, which can result in serious damages or even personal injuries.
It is also known in the art that a widely used type of counterbalancing mechanism generally comprises a pair of spaced apart cable drums connected to cables, each cable being in turn connected to a lower opposite side edge of the garage door. The cable drums are usually mounted onto an overhead shaft which is supported above the door opening and is connected to one or more torsion springs which are each fixed to the shaft at one end, and secured to a fixed structure such as the wall for example at the other end, so that the cable drums are biased to rotate in a direction which winds the cables onto the drums and counteracts the weight of the door connected to the cables. The torsion springs are adjusted to properly balance the weight of the door so that minimal opening and closing efforts are required, either manually or when motor controlled. An example of a conventional cable-operated sectional door and its corresponding counterbalancing mechanism is shown in FIG. 1, the sectional door being shown provided with a chain hoist for raising and lowering the door.
It is also known in the art that certain garage doors are not always properly counterbalanced or simply are operated without the use of a counterbalancing mechanism. Since these doors are not properly counterbalanced or are simply not counterbalanced at all, they are either always pulling on the cables with a downward force due to the weight of the door, or have a tendency to move upwards because the counterbalancing force of their torsional springs is too strong. This type of situation is particularly dangerous when the door is raised or lowered by means of a conventional drive mechanism, such a manually-operated chain hoist for example, because an operator needs to continuously hold the chain of the hoist, otherwise the door may fall to the ground or move up in an uncontrolled manner with an increasing speed. Such a situation is dangerous and often arises suddenly, particularly in the case of commercial doors which are known to be heavier than residential doors, because as soon as the hand chain of the hoist slips away from an operator""s hand, its speed tends to increase to a level that is practically impossible and/or very unsafe to stop manually, thereby often resulting in the door raising up or dropping in a very undesirable manner, i.e. with an increasing speed, which often in turn results into serious damages and/or personal injuries. Indeed, not only is the door itself dangerous when falling or moving up in an uncontrolled manner because it may severely impact an item or a person, but also hand injuries are very likely to occur when an operator of the chain hoist attempts to regain control of the chain which often rotates much faster than the overhead shaft of the door.
There exist several prior art documents describing different drive mechanisms for use with sectional doors. Known to the Applicant are the following United Sates patents which describe different drive mechanisms and the safety devices used therewith: U.S. Pat. Nos. 1,621,951; 2,095,695; 2,878,865; 3,188,698; 3,637,004; 4,112,996; 4,669,775; 4,704,914; 4,721,146; 4,997,022; 5,022,452; 5,291,686; 5,482,103; 5,494,093; 5,971,055; 6,029,735; 6,042,158; 6,059,008; 6,070,641; and 6,123,134.
It is also known in the art that occasionally, for one reason or the other, one of the cable of the counterbalancing mechanism brakes or one of the elements holding such cables undergoes failure, leading to the garage door falling all the way down, potentially causing damages or personal injuries. There exist some systems that prevent the free falling of a garage door by breaking it in its track in the advent of a failure of the counterbalancing mechanism. There are also systems that stop the door (i.e. let it go up, but do not let it go down) in such circumstances. Finally, there are also systems that slow down the falling of the door in case of an emergency condition, such as a fire for example. However, there seems to be no drive mechanism which not only is used for raising and lowering a sectional door, such as garage doors and the like, but which also acts as a safety device for preventing an uncontrollable raising and/or lowering of the sectional door as a result of the aforementioned adverse situations.
Hence, in light of the above-discussed, there is a need for an improved drive mechanism which, by virtue of its design and components, would not only be able to raise and lower a sectional door, such as garage doors and the like, but would also act as a safety device for preventing an uncontrollable raising and/or lowering of the sectional door, whether the latter be balanced, unbalanced or improperly balanced.
The object of the present invention is to provide a drive mechanism which satisfies some of the above-mentioned needs and which is thus an improvement over the devices known in the prior art.
In accordance with the present invention, the above object is achieved with a drive mechanism for use with an overhead shaft of a sectional door for raising and lowering said door via a rotation of the overhead shaft, the drive mechanism comprising:
support means through which the overhead shaft is pivotally inserted;
a first gear securely mounted about the overhead shaft of the sectional door;
a drive shaft pivotally mounted to the support means;
a second gear securely mounted about the drive shaft, the second gear being operatively interconnected to the first gear so that a rotation of the second gear is transmitted to the first gear and vice versa, the second gear being rotatable along a first direction corresponding to a raising of the sectional door and along an opposite second direction corresponding to a lowering of the sectional door;
a pocket wheel mounted about the drive shaft and being rotatably movable therealong between a first position where the pocket wheel is away from the second gear and a second position where the pocket wheel is operatively secured against the second gear and where further rotation of the pocket wheel biases the second gear to rotate along the first direction; and
actuating means for rotating the pocket wheel about the drive shaft, operating the said pocket wheel between the first and second positions, and driving the second gear along the first and second directions when the pocket wheel is in the first and second positions respectively.
According to a first preferred embodiment of the invention, the drive mechanism comprises a single ratchet assembly for blocking rotation of the second gear along the second direction when the pocket wheel is in the second position.
According to a second preferred embodiment of the invention, the drive mechanism comprises a second ratchet assembly for blocking rotation of the second gear along the first direction when the pocket wheel is in the first position
The objects, advantages and other features of the present invention will become more apparent upon reading of the following non-restrictive description of preferred embodiments thereof, given for the purpose of exemplification only with reference to the accompanying drawings.